1. Field of the Invention
The present invention relates to an electronic timepiece for storing energy generated by a thermoelectric element at a secondary battery and operated by generated power as well as energy of the secondary battery, particularly to effective use of generated power in accordance with power conservation and means for appealing situation of power generation or deficiency in the energy of the secondary battery to a user.
2. Description of the Prior Art
FIG. 2 shows a view of a structure of a thermoelectric element used in a conventional electronic timepiece having a thermoelectric element. A number of n-type semiconductors 203 and p-type semiconductors 204 are installed between a heat absorbing side substrate 202 and a heat radiating side substrate 201. The n-type semiconductors 203 and the p-type semiconductors 204 are alternately and electrically connected in series by electrodes 205 installed at the heat absorbing side substrate 202 and the heat radiating side substrate 201 and both ends thereof are led out as leads 206. A heat flow is flowed through the n-type semiconductors 203 and the p-type semiconductors 204 in parallel.
The heat absorbing side substrate 202 is thermally coupled with a rear lid of the electronic timepiece in touch with the user""s arm the temperature of which is generally higher than air temperature. The heat radiating side substrate 201 is thermally coupled with a timepiece case radiating heat to the atmosphere. When a temperature difference is caused between the heat absorbing side substrate 202 and the heat radiating side substrate 201, an electromotive force is generated by the Seebeck effect.
Next, an explanation will be given of a construction of the conventional electronic timepiece having the thermoelectric element in reference to a block diagram of FIG. 14. Electromotive force of a thermoelectric element 101 having a structure shown by FIG. 2 is transmitted to a booster circuit 302, boosted by the booster circuit 302 and is stored in a storage mechanism 103. Electric energy stored in the storage mechanism 103 is supplied as power source of a timepiece unit 110. The timepiece unit 110 is constituted by an oscillation or oscillating circuit 105 using quartz having a frequency of 32 kHz or the like, a frequency dividing circuit 106 for dividing an oscillation signal thereof into a signal having a period of 1 Hz and so on, a display driving circuit 107 for driving a step motor for display in accordance with a divided output and a display unit 108 comprising a step motor, a wheel train and display hands.
According to the constitution of the conventional electronic timepiece having the thermoelectric element, when the thermoelectric element 101 generates electricity, power consumption of the timepiece unit 110 is supplied by energy from the thermoelectric element 101 and an extra amount thereof is stored in the storage mechanism 103. Meanwhile, when the electromotive force is not provided from the thermoelectric element 101, the storage mechanism 103 supplies power to the timepiece unit 110, energy held by the storage mechanism 103 is reduced and voltage of the storage mechanism 103 is gradually lowered. At this occasion, in a range of voltage by which the timepiece can be operated, naturally, energy necessary for the operation is taken out from the storage mechanism 103 and further, even after a motor is stopped and the operation of the timepiece is stopped, a certain degree of current flows, energy from the storage mechanism 103 continues being discharged and the voltage continues lowering. Further, when the voltage of the storage mechanism 103 is dropped to a degree of about 0.6 V by which current is not flowed to the timepiece unit 110, lowering of voltage is stopped and the voltage is substantially maintained.
According to the above-described conventional electronic timepiece having the thermoelectric element, when power generation of the thermoelectric element is stopped for a long period of time, the voltage of the storage mechanism is lowered to the degree of about 0.6 V and even when power generation of the thermoelectric element is restarted and starts to charge the storage mechanism, an extremely long time period is needed until the voltage reaches about 1.0 V by which the timepiece can be operated normally. Although a time period for voltage to reach 1.0 V is dependent on power generation capability and capacity of the charge mechanism, when the charge capacity is set to an amount for operating for six months, several days are required for voltage to reach 1.0 V.
When the timepiece is detached from the arm before voltage reaches about 1.0V which is voltage for operating the timepiece, the timepiece is immediately stopped without being able to utilize energy of the storage mechanism. That is, although in order to make the timepiece continue operating even when it is detached from the arm, power generation of the thermoelectric element needs to continue for several days, actually, the power generation is interrupted highly probably in the midst of power generation.
Further, there is a request for downsizing and thinning in an electronic timepiece and downsizing is also requested to a storage mechanism. Therefore, energy stored to the storage mechanism is reduced, a time period capable of maintaining operation of a timepiece circuit by energy of the storage mechanism is shortened and a probability of causing stoppage of the timepiece circuit becomes high. In order to reduce danger of stoppage of operation, power consumption of the timepiece circuit needs to reduce when a thermoelectric element does not generate electricity.
Further, it is preferable to inform stoppage of power generation to a user when the thermoelectric element stops generating electricity. Further, it is also preferable to inform a user that a remaining amount of energy of the storage mechanism is reduced. Further, it is preferable to carry out the display in a state in which power consumption is reduced more than in normal display.
As means for resolving the above-described problem, an electronic timepiece having a thermoelectric element according to the present invention is installed with a thermoelectric element, a storage mechanism for storing an electromotive force of the thermoelectric element or storing a power produced by boosting an output from the thermoelectric element by a booster circuit, an oscillating circuit, a frequency dividing circuit or a time information calculating circuit, a display driving circuit, a display unit and in addition thereto, a power monitoring circuit for monitoring a situation of at least either one of generated power and stored energy by measuring generated voltage or current of the thermoelectric element or output voltage or current of the booster circuit or voltage of the storage mechanism, and an operation stopping circuit or a display drive controlling circuit for controlling operation of the oscillating circuit or the frequency dividing circuit or the time information calculating circuit or the display driving circuit by a detected output of the power monitoring circuit. When the power monitoring circuit detects stoppage of power generation of the thermoelectric element or a deficiency in stored energy of the storage mechanism, in order to reduce power consumed in the electronic timepiece, operation of the oscillating circuit, the frequency dividing circuit or the time information calculating circuit or the display driving circuit is controlled by an ON/OFF control by the display drive controlling circuit or the operation stopping circuit.
Further, in the case of a timepiece in a so-to-speak analog display using motors, a wheel train and hands as a displayer, in a constitution having a motor for a hour hand and a minute hand and a motor for a second hand, when the power monitoring circuit detects lowering of at least either one of generated power and stored energy, the lowering is informed to a user by stopping only the motor for the second hand and power consumption is reduced.
Further, when the power monitoring circuit detects lowering of generated power, there is provided a counting circuit for counting a time period of duration of the lowering and when there is no power generation for a long period of time, operation of a timepiece circuit including the oscillating circuit is stopped and dissipation of a battery is prevented.